1. Field of the Invention
The present invention relates to secure access techniques, and more particularly to authentication using access cards.
2. Description of the Related Art
Physical access cards are often used as a security measure for preventing access by unauthorized personnel to a secure area such as an office suite. A simple form of a physical access card is an access card with a magnetic stripe that stores a digital password. When a user approaches a locked door and presents the access card to a card reader, the card reader reads the password from the magnetic stripe. The card reader may communicate with a central server to confirm the password, and/or to check if the user is listed in an approved access control list. The central server can then unlock a door for the user.
One weakness of this simple system is that if the password from the magnetic-stripe can be read and reproduced by a malicious party, then the malicious party may be able to use the password to gain unauthorized access. One approach for strengthening the security measures is to use access cards that are “smart” cards, with a built-in processor and memory. A password, or key, is stored into the memory in such a manner that it can be read by the built-in processor, but cannot be read by a malicious party.
When a smart card is used to gain access to a secure area, the smart card can respond in real time to a “challenge” received from a card reader. The card reader typically uses random numbers to generate challenges that are unique: the challenges include data that are different from one access attempt to another. The smart card performs a calculation using its internally stored key and the data received from the card reader, and transmits a response, based on that calculation, back to the card reader. The card reader examines the response to confirm that the smart card possesses the correct key. Access is granted only if the smart card returns an acceptable response to the challenge sent by the card reader. This challenge-response interaction protects the key on the smart card: the key itself is not transmitted as part of the communications between the smart card and the card reader.
Such smart cards are generally more difficult to reproduce or simulate than a magnetic-stripe card. One of the concerns in such smart card authorization systems is that a malicious party may be able to deduce the internal key or otherwise “break” the cryptographic features in the calculations performed by the smart-card, and thereby provide acceptable responses to challenges from card readers. One approach to avoiding such attacks is to increase the sophistication of the challenge-response calculations performed by the smart-card. Such an approach generally imposes some additional cost, such as an increased processing power for the smart card. System designers, therefore, must generally make trade-offs between various costs and cryptographic security.